fix: persistent random Snowflake worker ID + clean reaction API

Two fixes addressing architectural review feedback:

1. Snowflake ID collisions: Replace process.pid-based worker ID with a
   cryptographically random value (0-1023) generated once at first boot
   and persisted to instance_settings.worker_id. Eliminates deterministic
   ID collisions between Docker instances that all run as PID 1.

2. Reaction API leak: Revert addReaction/removeReaction signatures to
   (messageId, emoji) — the store now resolves the channel internally by
   scanning its message cache, keeping routing logic out of the UI layer.

packages/web/src/components/chat/Message.tsx

@@ -60,9 +60,9 @@ export function Message({ message, isCompact, isFirstInGroup }: MessageProps) {
   const toggleReaction = (emoji: string) => {
     const hasReacted = message.reactions?.some(r => r.userId === currentUser?.id && r.emoji === emoji);
     if (hasReacted) {
-      removeReaction(message.id, emoji, channelKey);
+      removeReaction(message.id, emoji);
     } else {
-      addReaction(message.id, emoji, channelKey);
+      addReaction(message.id, emoji);
     }
   };
 

packages/web/src/stores/chatStore.ts

@@ -43,8 +43,8 @@ interface ChatState {
   addRealtimeMessage: (channelId: string, message: MessageWithUser) => void;
   updateMessage: (message: MessageWithUser) => void;
   removeMessage: (messageId: string, channelId: string) => void;
-  addReaction: (messageId: string, emoji: string, channelId: string) => void;
-  removeReaction: (messageId: string, emoji: string, channelId: string) => void;
+  addReaction: (messageId: string, emoji: string) => void;
+  removeReaction: (messageId: string, emoji: string) => void;
   onReactionAdded: (messageId: string, reaction: any) => void;
   onReactionRemoved: (messageId: string, userId: string, emoji: string) => void;
   setTyping: (channelId: string, userId: string, username: string) => void;
@@ -57,6 +57,16 @@ interface ChatState {
   onChannelAck: (channelId: string, messageId: string) => void;
 }
 
+/** Find which channel a message belongs to by scanning the message cache. */
+function findChannelForMessage(messages: Map<string, MessageWithUser[]>, messageId: string): string | null {
+  for (const [channelId, msgs] of messages) {
+    if (msgs.some(m => m.id === messageId)) {
+      return channelId;
+    }
+  }
+  return null;
+}
+
 export const useChatStore = create<ChatState>((set, get) => ({
   messages: new Map(),
   currentChannelId: null,
@@ -356,13 +366,16 @@ export const useChatStore = create<ChatState>((set, get) => ({
     });
   },
 
-  addReaction: (messageId: string, emoji: string, channelId: string) => {
-    const origin = getChannelOrigin(channelId);
+  addReaction: (messageId: string, emoji: string) => {
+    // Resolve the channel from our message cache so the UI doesn't need to pass it
+    const channelId = findChannelForMessage(get().messages, messageId);
+    const origin = channelId ? getChannelOrigin(channelId) : '';
     wsSend({ type: 'reaction_add', messageId, emoji }, origin);
   },
 
-  removeReaction: (messageId: string, emoji: string, channelId: string) => {
-    const origin = getChannelOrigin(channelId);
+  removeReaction: (messageId: string, emoji: string) => {
+    const channelId = findChannelForMessage(get().messages, messageId);
+    const origin = channelId ? getChannelOrigin(channelId) : '';
     wsSend({ type: 'reaction_remove', messageId, emoji }, origin);
   },